Most gain blocks are intended to be used without additional matching. For these amplifiers the power gain (Gp) is also equal to |S21|2 (The unmatched gain in a 50 ohm system). Some ICs are intended to be used with additional matching and the gain specified may be a tuned gain depending on this matching. If the matching provides an optimal noise match to the input and a conjugate (optimal gain) match to the output, then the gain is called associated gain (Ga).

The input power Pin (in dBm) is equal to Pout (in dBm) - Gp (in dB). Some amplifiers are designed to have their gain adjusted by a control voltage; these devices will typically have a gain control range (GCR) specified. The GCR is the amount by which the gain may be decreased from the maximum gain in dB. Typical GCR's are in the 20 - 30 dB range though ranges as high as 50 dB may be encountered. Gain decreases with frequency and increases with bias.

Direction:

Needs to fit application. More gain means less stages but too much gain can lead to stability problems or saturation. In general more is better.